Combustion mixture control system for calenders

ABSTRACT

A combustion mixture control system for heated rolls used in calenders and embossers. This system employs a technique for sampling the air pressure and the combustion mixture pressure in conjunction with the use of a discrete timer for control of a fuel zero regulator to thereby control the composition of the combustion mixture applied to the calender roll burner. By thus controlling the amount of fuel in the fuel/air mixture greater efficiency of operation is achieved and resonant noise often associated with initial heating is abated.

United States Patent Rauskolb 51 Oct. 17, 1972 [5 COMBUSTION MIXTURE CONTROL 3,119,603 1/1964 Schaab et a1 ..263/6 C SYSTEM FOR CALENDERS [72] Inventor: Fred W. Rauskolb, l-laworth, NJ. Pnmary Examiner-Charles Myhre [73] Assignee: Standard International Corporation, [57 ABSTRACT Andover, Mass. A combustion mixture control system for heated rolls [22] June 14, 1971 used in calenders and embossers. This system employs 2 Appl 52 a technique for sampling the air pressure and the combustion mixture pressure in conjunction with the use of a discrete timer for control of a fuel zero regulator [52] US. Cll. ..263/6 C to thereby control the composition of the combustion mixture the Calender roll burnerthus I 1 [e d 0 can: C, 6 R n ol ing th ount of fuel in e uel/air mixture greater efficiency of operation is achieved and reso- [56] References cued nant noise often associated with initial heating is UNITED STATES PATENTS abated- 2,987,305 6/1961 Calhoun, Jr ..263/6 C 7 Claims, 1 Drawing Figure AIR 1N PILOT PILOT N23 BURNER -13 UR I4 267 25 I5 M'XER 12 5 s i q gc iR 3-WAY VALVE T1MER M7 21 l ZERO START courEoL AND SAFETY EQUIP.

COMBUSTION MIXTURE CONTROL SYSTEM FOR CALENDERS FIELD OF THE INVENTION This invention relates in general to calenders and embossers and more particularly concerns an improved carburetion system for preventing noise from occurring during the initial heating period of the heated rolls used in such machines.

DISCUSSION OF THE PRIOR ART of heating time after the burner is started, an extremely loud resonant vibration occurs caused by the rapid change in temperature and the movement of .air throughout the length of this large tube. During this time, the roll and burner act much like an organ pipe, thereby creating a deafening sound which is characteristic of many heated roll machines.

The normal manner for applying combustion mixture to a burner for heating a roll of this type is to supply a relatively rich fuel mixture which may be fired by a conventional pilot burner flame or spark generator. Once started, the flame continues throughout the length of the roll along the burner therewithin, thus heating the roll from the interior. The noise often associated with this procedure normally lasts from 3 to 5 minutes and then does not again occur until the roll has cooled and is once again heated. However, the noise is so loud and uncomfortable during that relatively short startup period that it is highly desirable to prevent it from occurring at all. Furthermore, noise abatement regulations proposed or now effective will require noise of this type to be substantially abated in some manner.

SUMMARY OF THE INVENTION This invention comprises a carburetion system which initially provides a fuel/air combustion mixture sufficient for ignition of the burner and thereafter changes the mixture to improve the efficiency of the burner and therefore the overall efficiency of calendering and embossing machines using heated rolls. Not only does this novel calender roll heating system improve operating efficiency, it substantially prevents the aforesaid noise normally associated with initial heating. This system also uses conventional equipment including appropriate pilots, flame rods, temperature sensors, controllers, burners and safety cutoff features. The invention is concerned with that portion of the heating system which controls the fuel/air mixture applied to the burner.

A three-way valve samples the incoming air before it reaches the mixer and alternatively samples the combustion mixture pressure between the mixer and the burner, depending upon the position of the three-way valve as controlled by a timer. The timer may control the valve through a solenoid or other suitable means. This valve applies the sampled pressure to the fuel zero regulator which in turn controls the amount of fuel entering the mixer, thereby controlling the combustion mixture constituent percentages. In response to the sampled air or combustion mixture pressures, it is thus seen that the valve controls the amount of fuel applied to the mixer, thereby affecting the richness or leanness of the combustion mixture. By thus maintaining positive control of thecombustion mixture in relation to time of ignition, the resonant noise previously mentioned is effectively controlled.

For simplicity of terminology, the word calender is used herein to include calendering and embossing machines, and it will be presumed that natural gas is the fuel used in the combustion mixture, even though other fuels might be satisfactory.

BRIEF DESCRIPTION OF THE DRAWING The objects, advantages and features of this invention will become apparent from the following detailed description when read in conjunction with the accompanying drawing in which TI-IE FIGURE shows a schematic diagram of a novel combustion mixture control system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The drawing depicts a calender roll 11 with a typical internal burner 12 along the axis of the roll extending from either end thereof. A substantial margin normally exists between the burner and the interior wall of the roll throughout its length. This readily permits exhaust gases to escape at either end of the roll. A pilot burner 13 is a conventional unit which is normally, in a gas burner, a continuously burning gas flame. Other ignition devices could be used if desired. The pilot flame is applied at the end of the roll cavity alongside burner 12 as indicated by reference numeral 14. Burner 12 may have any suitable configuration including those presently used which emit the combustion mixture from a slit or a multiplicity of ports or tips along its length.

The combustion mixture is applied in a conventional manner to end 15 of burner 12 and passes down the length of the burner to be projected outwardly through the burner slots, holes or tips. Before ignition this combustion mixture travels outward toward either end of the roll, escaping from the marginal areas between the roll cavity and the burner. Shortly after gas is applied to the combustion air to form a combustible mixture, the pilot flame ignites the mixture emitted from the end of the roll and the flame consequently passes down the length of the burner thereby commencing heating of the roll. In order for ignition to occur, the combustion mixture applied at end 15 of burner 12 must be relatively rich, that is, it should normally have greater than 12 per cent gas. This is necessary so that when it mixes with the air within the burner and returns to the end in the vicinity of the pilot flame in somewhat diluted form, it will be still easily ignitable. In most present heated roll calenders, the initial combustion mixture continues to be applied to the burner, no change in the percentage of the constituents being made after the gas is initially turned on. By continuing to apply a rich mixture, undiluted during normal operation because it is burned as it is emitted from the burner along its length, the previously described howling noise starts very shortly after ignition and continues at a very intense level for several minutes.

The exact cause of the objectionable noise is not clear but it is thought to be a result of the combination of many factors including the long tube of the interior of the roll, the rapid heating of the air therein and the surface material thereof, and the motion toward the ends of the tube by the gaseous mixture caused by its rapid expansion. It is believed that all of these factors contribute to the creation of resonant vibrations which continue until equilibrium is established within the tube and when the only significant change continuing to occur is the steady increase in roll temperature.

in order to appreciate the order of magnitude of the noise created, it is well to realize that the roll may be approximately l32 inches long and 20 inches in diameter with a 4 inch diameter center bore through its full length and walls of solid steel 8 inches thick. Such a roll may weigh between 10,000 and 28,000 pounds. with such dimensions, it may be realized that when resonance is achieved, it will be intense.

For purposes of preventing the occurrence of the loud resonant vibrations presently being experienced during the initial heating of calender rolls, this invention carefully controls the percentages of the constituents in the combustion mixture. When start switch 16 is initiated, timer l7 commences a predetermined timing period and plural position three-way valve 21 is set to its first position. In the first position, the valve samples the incoming air pressure ahead of mixer 22 as shown by junction 23. This relatively high air pressure, adjusted by pressure adjusting valve 28, is applied through the valve to zero regulator 24, thereby causing a relatively large amount of gas to be applied to mixer 22 to form a suitable rich combustion mixture. Combustion can take place with a gas percentage of between 4 and 12 percent but, as stated previously, a

' rich mixture is necessary to facilitate ignition.

For optimum operating efficiency, the mixture should be less than 12 percent gas, the normal stoichiometric mixture having percent gas which permits complete combustion. The term stoichiometric as herein used refers to an ideal combustion mixture having sufficient combustion air to completely burn all of the gas. It will immediately be recognized that combustion mixtures having higher than stoichiometric gas percentages may be termed rich mixtures. Such mixtures are somewhat inefficient because there is insufficient oxygen available for complete combustion and because the flame may be too long for proper heating. At the end of the predetermined timing period, timer 17 switches three-way valve 21 to its second position to sample the pressure of the combustion mixture entering burner 12 as shown at junction 25. This pressure will normally be less than the properly regulated incoming air pressure and the zero regulator responds by decreasing the volume of gas applied to mixer 22 resulting in a somewhat leaner combustion mixture. It has been found that by changing from a rich to a stoichiometric mixture immediately after ignition of the main burner, the objectionable resonant vibrations never commence and no additional noise abatement equipment is necessary.

Gas zero regulator 24 is a standard regulator which is continuously variable in response to the pressure applied through valve 21 and therefore continuously controls the amount of gas in relation to the pressure of the combustion mixture entering burner 12. Timer 1'! is a conventional device having a set time period which may be varied as desired within reasonable limits. Under normal starting conditions with the pilot light on, it would be expected that the main burner would be lighted at least within 10 to 15 seconds after. the start switch is activated. The timer is set for the appropriate time period within which it is reasonably expected that the main burner will be completely ignited and burning properly. At the expiration of. that time the timer causes changes to occur in the combustion mixture as previously described.

Temperature sensor 26 is shown connecting to control and safety equipment 27, all using conventional apparatus. The control and safety equipment includes various items not otherwise shown such as flame detecting rods, safety shut off valves and blocking valves in a conventional arrangement as required for purposes of safety. Sensor 26 also includes the necessary means for the temperature control and high temperature cutoff when combined with control 27. Since these elements do not form a material part of this invention but are only part of the entire heated roll system, they will not be further described herein.

The system described herein provides combustion mixtures with the appropriate constituencies and at the appropriate times to provide efficient heating of the calender roll while at the same time preventing the characteristic howling noise often associated with the heating of such rolls. The twofold advantages of this system are thus apparent and the simplicity of the structure with which these advantages are achieved is in itself a feature of the invention.

There are several modifications of the calender machine embodiment shown in the drawing which may employ the invention. The drawing shows a double ended system having a pilot burner at each end of the roll with combustion mixture entering the burner from both ends. Burners of this type may be continuous throughout their length or they may have a center partition so that each half of the burner on either side of center is operated independently. This would normally require duplication of controls so that individual portions of the burner may be adjusted to achieve balance in the heating of the roll. If the baffle or center partition is not used, the embodiment shown in the drawing is satisfactory. Another alternative embodiment and one that is often used is a structure employing a single pilot burner at one end with the combustion mixture entering only at that end. As mentioned previously, the burner may be a conventional one of the type presently used for heating calender rolls.

It may readily be seen that other modifications to the roll heating system may be made which are within the scope of this invention.

What is claimed is;

1. A combustion mixture control system for a heated calender roll having a burner passing therethrough, comprising:

means for supplying air to said system;

means for supplying fuel to said system;

a mixer for combining and mixing the air and fuel supplied to said system;

conduit means for conducting the air/fuel mixture from said mixer to said burner;

timing means; and

means responsive to said timing means for controlling the percentage of fuel in said mixture, said controlling means providing a mixture having a first percentage of fuel when the system is actuated and providing a mixture having a second percentage of fuel after a predetermined period of time.

2. The combustion mixture control system recited in claim 1 wherein:

said controlling means includes:

a fuel zero regulator adapted to vary the volume of fuel applied to said mixer in response to said air and said mixture pressures selectively applied to said zero regulator;

a plural position valve for connecting the pressure sensitive portion of said zero regulator to appropriate conduits for said air and said mixture to thereby control said zero regulator, the position of said valve being governed by said timer.

3. The combustion mixture control system recited in claim 2 and further comprising a start switch for activation of said system to commence heating of said calender roll.

4. The combustion mixture control system recited in claim 3 wherein one side of said valve is connected ahead of said mixer to sample incoming air pressure and another side is connected to said conduit means between said mixer and said burner to sample the pressure of said fuel mixture, said valve applying said incoming air pressure to said zero regulator when in a first position and applying said mixture pressure to said zero regulator when in a second position.

5. The combustion mixture control system recited in claim 4 wherein actuation of said start switch commences said timer and places said valve in said first position;

upon expiration of said predetermined period of time, said timer causes said valve to shift to said second position.

6. A combustion mixture control system for a heated calender roll having a burner passing therethrough, comprising a start switch;

a timer adapted to be set for a predetermined time period;

a three-way valve having a first position and a second position, the position of said valve being responsive to said timer; a fuel zero regulator;

means for supplying fuel to said zero regulator;

a mixer for forming a combustion mixture of air and fuel;

first conduit means for supplying incoming air to said mixer;

second conduit means for transmitting fuel from said zero regulator to said mixer; and

third conduit means for transmitting said combustion mixture from said mixer to said burner;

said zero regulator being sensitive to gas pressures, the amount of fuel transmitted to said mixer being responsive to pressures applied thereto through said valve;

said valve being connected to said zero regulator, said first conduit means and said third conduit means, said valve when in said first position applying incoming air pressure to said zero regulator and when in said second position applying said combustion mixture pressure to san zero regu ator, said valve being in said first position when said start switch is activated and being changed to said second position by said timer upon expiration of said predetermined period of time;

said combustion mixture being stoichiometric during normal operation of said system when said valve is in said second position and having greater than the stoichiometric percentage of gas when said valve is in said second position.

7. A combustion mixture control system for a heated calender roll having a burner passing therethrough, 

1. A combustion mixture control system for a heated calender roll having a burner passing therethrough, comprising: means for supplying air to said system; means for supplying fuel to said system; a mixer for combining and mixing the air and fuel supplied to said system; conduit means for conducting the air/fuel mixture from said mixer to said burner; timing means; and means responsive to said timing means for controlling the percentage of fuel in said mixture, said controlling means providing a mixture having a first percentage of fuel when the system is actuated and providing a mixture having a second percentage of fuel after a predetermined period of time.
 2. The combustion mixture control system recited in claim 1 wherein: said controlling means includes: a fuel zero regulator adapted to vary the volume of fuel applied to said mixer in response to said air and said mixture pressures selectively applied to said zero regulator; a plural position valve for connecting the pressure sensitive portion of said zero regulator to appropriate conduits for said air and said mixture to thereby control said zero regulator, the position of said valve being governed by said timer.
 3. The combustion mixture control system recited in claim 2 and further comprising a start switch for activation of said system to commence heating of said calender roll.
 4. The combustion mixture control system recited in claim 3 wherein one side of said valve is connected ahead of said mixer to sample incoming air pressure and another side is connected to said conduit means between said mixer and said burner to sample the pressure of said fuel mixture, said valve applying said incoming air pressure to said zero regulator when in a first position and applying said mixture pressure to said zero regulator when in a second position.
 5. The combustion mixture control system recited in claim 4 wherein actuation of said start switch commences said timer and places said valve in said first position; upon expiration of said predetermined period of time, said timer causes said valve to shift to said second position.
 6. A combustion mixture control system for a heated calender roll having a burner passing therethrough, comprising a start switch; a timer adapted to be set for a predetermined time period; a three-way valve having a first position and a second position, the position of said valve being responsive to said timer; a fuel zero regulator; means for supplying fuel to said zero regulator; a mixer for forming a combustion mixture of air and fuel; first conduit means for supplying incoming air to said mixer; second conduit means for transmitting fuel from said zero regulator to said mixer; and third conduit means for transmitting said combustion mixture from said mixer to said burner; said zero regulator being sensitive to gas pressures, the amount of fuel transmitted to said mixer being responsive to pressures applied thereto through said valve; said valve being connected to said zero regulator, said first conduit means and said third conduit means, said valve when in said first position applying incoming air pressure to said zero regulator and when in said second position applying said combustion mixture pressure to said zero regulator, said valve being in said first position when said start switch is activated and being changed to said second position by said timer upon expiration of said predetermined period of time; said combustion mixture being stoichiometric during normal operation of said system when said valve is in said second position and having greater than the stoichiometric percentage of gas when said valve is in said second position.
 7. A combustion mixture control system for a heated calender roll having a burner passing therethrough, comprising: means for supplying a combustion mixture of fuel and air to said burner; means for controlling the percentage of fuel in said combustion mixture; and timing means; said controlling means being responsive to said timing means for initially supplying a combustion mixture having a greater than stoichiometric percentage of fuel and then reducing said fuel to provide a stoichiometric combustion mixture to said burner after ignition of said burner. 